This section provides background information related to the present disclosure which is not necessarily prior art.
Many internal combustion engines utilize cylinder liners or sleeves. Such internal combustion engines generally include an engine block having one or more cylinders. A piston is disposed within each cylinder when the internal combustion engine is fully assembled. Cylinder liners, which are generally cylindrical in shape, are positioned within the cylinder of the internal combustion engine between the piston and the engine block. Accordingly, the piston does not directly contact the engine block. Although cylinder liners often add complexity to the engine block, cylinder liners have many advantages. The cylinder liner presents a wear surface that can be replaced in the event of excessive wear. Excessive wear may occur in internal combustion engines that experience piston or ring failure. In such instances, the internal combustion engine can be more easily repaired without the need for re-boring and honing the engine block or replacing the engine block altogether. Cylinder liners can also be made from a different material than the material used in the engine block. Accordingly, the engine block can be made of a lighter, more brittle material such as aluminum to save weight, while the cylinder liner can be made of a heavier, stronger material such as cast iron to improve thermodynamics and durability.
One design problem that arises in internal combustion engines that utilize cylinder liners is how to effectively draw heat away from the cylinder liners. Cylinder liners are exposed to combustion and therefore are subject to high thermal loads. The cylinder liners themselves are relatively thin and often conduct heat better than the adjacent material of the engine block, making thermal management of the cylinder liner difficult. One solution to this problem is commonly referred to as a “wet liner” arrangement. In this arrangement, at least part of the cylinder liner is placed in direct contact with coolant water or a water and anti-freeze solution. The coolant water or water and anti-freeze solution flows through a water jacket disposed between at least a portion of the cylinder liner and the engine block. Thermal management is achieved more readily because heat from the cylinder liner is transferred directly to the coolant water or water and anti-freeze solution. The coolant water or water and anti-freeze solution in the water jacket is replenished so that heat is continuously being drawn away from the cylinder liner. Water is used as a coolant because water has a very high specific heat capacity, a high density, and exhibits good thermal conductivity. As a result, high heat transfer coefficients can be achieved when water or a water and anti-freeze solution is used to cool the cylinder liners of internal combustion engines.
The use of water or a water and anti-freeze solution as an engine coolant does have some drawbacks however. Corrosion of metal components increases significantly when such components are exposed to water. As a result, water coolant can corrode elements of the engine coolant system and surfaces of the water jacket passages. Should a leak occur, corrosion of other engine components is also likely to occur. If the leak is inside the engine, other problems can develop. Water does not combine with gas or oil. Therefore, water inside the engine can displace the oil and create excessive wear because, unlike oil, water is not a lubricant. These problems are exaggerated in opposed-piston engines because of the sealing difficulties associated with the layout and packaging of opposed-piston engines.
Opposed-piston engines generally include two pistons housed within each cylinder that move in an opposed, reciprocal manner within the cylinder. In this regard, during one stage of operation the pistons are moving away from one another within the cylinder and during another stage of operation the pistons are moving towards one another within the cylinder. As the pistons move towards one another within the cylinder, they compress and, thus, cause ignition of a fuel/air mixture disposed within the cylinder. In so doing, the pistons are forced apart from one another, thereby exposing the inlet port and the exhaust port. Exposing the inlet port draws air into the cylinder and this in combination with exposing the exhaust port expels exhaust, thereby allowing the process to begin anew. When the pistons are forced apart from one another, connecting rods respectively associated with each piston transfer the linear motion of the pistons relative to and within the cylinder to two crankshafts disposed on opposite sides of the cylinder. The longitudinal forces imparted on the crankshafts by the connecting rods cause rotation of the crankshafts which, in turn, cause rotation of wheels of a vehicle in which the engine is installed.
Generally speaking, opposed-piston engines include a bank of cylinders with each cylinder having a pair of pistons slidably disposed therein. While the engine may include any number of cylinders, the particular number of cylinders included is generally dictated by the type and/or required output of the vehicle. For example, in an automobile, fewer cylinders may be required to properly propel and provide adequate power to the vehicle when compared to a heavier vehicle such as a commercial truck, a ship, or tank. Accordingly, a light vehicle may include an engine having three (3) cylinders and six (6) pistons while a heavier vehicle may include five (5) or six (6) cylinders and ten (10) or twelve (12) pistons, respectively.
Such opposed-piston engines typically have a one-piece engine block (i.e. made from a single casting). The opposed-piston engine includes two crankcases, one disposed to one side of the cylinders and the other disposed on an opposite side of the cylinders. The two crankshafts are supported in the two crankcases for rotation therein. A cylinder liner may be inserted into each of the cylinders from one crankcase or the other. In order to properly accommodate and seal the cylinder liner in the one piece engine block, complicated machining in the cylinder and/or the cylinder liner is required because access to these areas is limited, making it difficult to seal the inlet and exhaust ports in the cylinder liner. As such, the inlet and exhaust ports present an entry point through which water can leak out of the water jacket and into the combustion chamber.